Any mutagenesis assay aimed at elucidating the factors leading to an increased incidence of cancer and purporting to play a relevant role in cancer risk assessment should preferably be applicable to several species, i.e. mouse, rat and human. The existence of a cellular pathway with gene(s) that have been evolutionarily conserved from nematodes to man provide the potential to determine mutant frequencies in virtually any organ of any vertebrate species. All parts for the development of an eukaryotic mutagenesis assay based on an evolutionary conserved, expressed gene are readily available and have been characterized in some detail. Such an assay would be of great value to human cancer risk assessment and the extrapolation of mutagenicity data between species. It is anticipated that the successful development of this new in vivo model will provide a unique opportunity to study in vivo mutant frequencies in human tissues and cell lines established from human tissues. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE